This invention relates to an instrument for determining visual surface properties, i.e. for physically objectivating surface properties as they are perceived by the human eye by physiologically and psychologically processing spectrally weighted reflected or scattered radiation, radiation subjected to interference, or fluorescence radiation, which originates from surfaces of objects. Examples of such surface properties are gloss, haze, fogging, colour, metal-effect, mother-of-pearl effect, etc. In order to follow the valuation functions of the eye, an instrument of this type must be capable quantitatively to detect the angular, phase and spectral distribution of the radiation remitted by the surface, based on a given geometry and spectral composition of the radiation incident on the surface. For all practical cases, one single measurement geometry will be insufficient to perform this task.
An instrument for determining visual properties of a surface, which comprising a source emitting a beam of radiation, a detector, and an optical system for directing the beam emitted by the radiation source onto the surface and the beam remitted from the surface onto the detector, is known from Austrian Patent Specification No. 356,935. In this instrument, the optical illumination and measurement system includes a lens and a bundle of optical fibres arranged along an axis that extends perpendicularly to the surface under examination the fibre bundle is split into a number of partial bundles for supplying the reflected light to a corresponding number of detectors. Different angles of illumination and reflection may be obtained only by tilting the instrument with respect to the surface.
"International Laboratory", September 1990, pages 28 to 32, discloses another instrument for determining visual surface properties, which comprises three measuring arrangements in which the angles of incidence and reflection, related to the normal of the surface under examination, are 20.degree./20.degree., 60.degree./60.degree., and 85.degree./85.degree.. Each of these three measuring arrangements includes a radiation source, a first optical system which directs the beam emitted by the radiation source onto the surface, a detector, and a second optical system which directs the beam remitted by the surface onto the detector. The large number of optical components required renders the known instrument complicated and expensive. Moreover, the known instrument has a considerably long basic surface to be placed on the surface under examination, so that it permits measurements only on correspondingly large, or freely accessible, plane surfaces.
Other prior-art instruments use one single measurement geometry only and are accordingly less complicated and smaller. For a complete valuation of the visual surface properties, however, a plurality of such instruments with different geometries are required, which results in even higher overall expenses.